From 493a1fcbe052b795fab26629f9c5161b0703714b Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 17 Feb 2010 00:41:53 +0000
Subject: [PATCH] Don't attempt to divide INT_MIN by -1; consider such cases to
 have overflowed.

llvm-svn: 96428
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp |  4 +++
 test/CodeGen/X86/lsr-overflow.ll             | 26 ++++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 test/CodeGen/X86/lsr-overflow.ll

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index dddc65a1d0d..9d11876c21d 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2112,12 +2112,16 @@ void LSRInstance::GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx,
     Formula F = Base;
 
     // Check that the multiplication doesn't overflow.
+    if (F.AM.BaseOffs == INT64_MIN && Factor == -1)
+      continue;
     F.AM.BaseOffs = (uint64_t)Base.AM.BaseOffs * Factor;
     if ((int64_t)F.AM.BaseOffs / Factor != Base.AM.BaseOffs)
       continue;
 
     // Check that multiplying with the use offset doesn't overflow.
     int64_t Offset = LU.MinOffset;
+    if (Offset == INT64_MIN && Factor == -1)
+      continue;
     Offset = (uint64_t)Offset * Factor;
     if ((int64_t)Offset / Factor != LU.MinOffset)
       continue;
diff --git a/test/CodeGen/X86/lsr-overflow.ll b/test/CodeGen/X86/lsr-overflow.ll
new file mode 100644
index 00000000000..eb6fa905b5a
--- /dev/null
+++ b/test/CodeGen/X86/lsr-overflow.ll
@@ -0,0 +1,26 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+; The comparison uses the pre-inc value, which could lead LSR to
+; try to compute -INT64_MIN.
+
+; CHECK: movabsq $-9223372036854775808, %rax ## imm = 0x8000000000000000
+; CHECK: cmpq  %rax, %rbx
+; CHECK: sete  %al
+
+declare i64 @bar()
+
+define i1 @foo() nounwind {
+entry:
+  br label %for.cond.i
+
+for.cond.i:
+  %indvar = phi i64 [ 0, %entry ], [ %indvar.next, %for.cond.i ]
+  %t = call i64 @bar()
+  %indvar.next = add i64 %indvar, 1
+  %s = icmp ne i64 %indvar.next, %t
+  br i1 %s, label %for.cond.i, label %__ABContainsLabel.exit
+
+__ABContainsLabel.exit:
+  %cmp = icmp eq i64 %indvar, 9223372036854775807
+  ret i1 %cmp
+}